1. Field of the Invention
The present application relates to a semiconductor apparatus, in particular, the application relates to a power amplifier including semiconductor devices.
2. Related Background Arts
A power amplifier including a plurality of transistors each connected in series has been well known in the field. A multi-stage architecture of the semiconductor transistors is preferable to obtain a desirable gain. A Japanese patent application published as JP-H06-232661A has disclosed such a multi-stage power amplifier.
Recently, nitride semiconductor materials such as GaN, AlGaN, and so on, have been attracted because of their excellent voltage endurance. However, nitride based transistors show linearity insufficient for some applications. For instance, a multi-stage power amplifier constituted by nitride based transistors show far insufficient linearity.
On the other hand, transistors primarily comprised of GaAs based material such as GaAs, InGaAs, and so on show acceptable linearity when they are installed in a multi-stage power amplifier, but the output power thereof is still insufficient compared with those constituted by nitride transistors. A practical combination of GaAs based transistor with nitride transistors has been expected in the field.